New York, March 19: The Manhattan address of Eric, son of presidential nomination frontrunner Donald Trump, on Thursday received an envelope that contained a suspicious white powder compelling officials to investigate into it.

Later, it was officially confirmed that the white substance was not hazardous and there were no injuries.

According to law enforcement sources, the letter threatened the Trump family over Donald's presence in the race for the presidential nomination. The letter said that if Donald Trump did not pull out of the race for the Republican nomination, the next envelope would not be fake, an ABC& Eyewitness News report said. The letter bore the sign 'X', the news report said.

The letter had the postmark of March 5 and was posted from Boston. It was opened by Eric Trump's wife Lara, the report added.

The FBI was leading the probe and working with other agencies like the US Secret Service, Postal Inspector and the New York Police.

Eric Trump is the younger son of Donald and was seen campaigning for his father in this year's presidential election.

'Anonymous' video targets Trump:

Also on the same day, a hacking group known as "Anonymous" posted a video targeting Trump and called him a Nazi.

Only Donald Trump gets protection from the Secret Service now. However, his family was briefed earlier about proper handling of mail.